Distribution of weak bases between anhydrous acetonitrile and crosslinked polystyrenesulfonic acids. Separation of basicity, capacity and selectivity effects. Nonaqueous ion exchange chromatography

Abstract

Distribution of weak bases between anhydrous acetonitrile and crosslinked polystyrenesulfonic acid ion exchange resins was studied at 25.0° over a wide concentration range. Analysis of the data afforded equilibrium constants and effective resin capacities for a variety of bases. Equilibrium constants so obtained correlate well with basicity for a series of m- and p-substituted acetanilides. Modification of the hydrocarbon portions of the base has little effect on the selectivity of the resin for the conjugate acid cation. This result is compared with the different behavior known for ion exchange equilibria with water solutions and deducible from selectivity effects in resin-catalysed ester hydrolyses in aqueous acetone. A physical model explaining the observation of reduced effective capacities, C, of the resins in contact with non-aqueous solvents was developed and the measured C values were correlated with structure. Principal determinants of C are solvent, crosslinking and ion size. Application of these results to chromatography on anhydrous ion exchangers in non-aqueous media is discussed and preliminary chromatographic results are presented.